Fungi are eukaryotic organisms that have characteristics distinct from other organisms, including plants, and are thus classified in their own kingdom. They differ from plants in that they contain chitin in their cell walls and do not utilize photosynthesis to obtain nourishment.
Fungi attain mobility mainly through growth, but also through the use of spores, which can travel through the air or water. Another characteristic is that they are the main decomposers in ecological systems.
The fungus kingdom, which includes yeasts, molds and mushrooms, is extremely diverse and contains an enormous number of species, with estimates ranging as high as 3.8 million. Of these, fewer than 150,000 have been described.